Reliably producing submicron and smaller features is one of the key technological challenges for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. However, as the miniaturization of circuit technology continues, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on the processing capabilities. For example, as circuit densities increase for next generation devices, the widths of interconnects, such as vias, trenches, contacts, gate structures and other features, as well as the dielectric materials therebetween, decrease while the thickness of the dielectric layers remains substantially constant, with the result of increasing the aspect ratios of the features.
Sputtering, also known as physical vapor deposition (PVD), is a commonly-used method of forming metallic features in integrated circuits. Sputtering deposits a material layer on a substrate. A source material, such as a target, is bombarded by ions strongly accelerated by an electric field. The bombardment ejects material from the target, and the material then deposits on the substrate. During deposition, ejected particles may travel in varying directions, rather than generally orthogonal to the substrate surface, thus resulting in overhanging structures formed on corners of high aspect ratio features in the substrate. Overhang may undesirably result in holes or voids formed within the deposited material, resulting in diminished electrical conductivity of the formed feature. Higher aspect ratio geometries have a higher degree of difficulty to fill without voids.
Controlling the ion fraction or ion density reaching the substrate surface to a particular range may improve the bottom and sidewall coverage during the metal layer deposition process (and reduce the overhang problem). In one example, the particles dislodged from the target may controlled via a process tool such as a collimator to facilitate providing a more vertical trajectory of particles into the feature. The collimator provides relatively long, straight, and narrow passageways between the target and the substrate to filter out non-vertically travelling particles which impact and stick to the passageways of the collimator.
The actual amount of filtering accomplished by a given collimator depends at least in part on the aspect ratio of the apertures through the collimator. As such, particles traveling on a path approaching normal to the substrate pass through the collimator and are deposited on the substrate, which improves coverage of the bottom of high aspect ratio features. However, certain problems exist with the use of prior art collimators, which typically have an overall hexagonal shape. Unfortunately, PVD chambers with a prior art collimator leave a six-point deposition near an edge of the substrate due to shadowing of the corners of the hexagonal collimator.
Thus, the inventors have provided improved embodiments of apparatus with improved deposition uniformity.